1. Field of the Invention
This invention relates to automatic document, e.g., paper sheet, feeder mechanisms, and particularly to automatically adaptable document feeders for reliable feeding of nonhomogenous, nonuniform stacks of documents.
2. Description of Related Art
Feeding sheets from the top of a vertically oriented stack of sheets using suckers or vacuum suction cups and puffer air is well known in the art. For example, U.S. Pat. Nos. 3,218,062 and 4,382,593 both show the use of a blow pipe or puffs of air to separate the top sheets of the stack, especially the top sheet, and vacuum pickers to provide reliable feeding of the top sheet only.
The '062 patent also includes a moveable, cam-operated feeder which is mechanically connected to the moveable vacuum suckers and the moveable blow pipe so that these elements are optimally positioned relative to the top of the stack.
The '593 patent uses a separator or restraining mechanical finger in the form of wires which act to hold down the top sheet's leading (or feed) edge as the sheet is elevated by the puffer air. In this way, the short wire members establish the pick-up zone for the feeder's suction cups. In addition, once the top sheet is vacuum attached to the suction cups, the cups move vertically upward to deliver the sheet to the lower horizontal surface of a vacuum transport belt.
U.S. Pat. No. 3,642,272 shows a device for separating the top sheet of a stack from the underlying sheets by use of a blower nozzle and suction means. In this patent, the top of the stack is sensed and a stack elevator is thereby controlled to maintain the stack's top sheet at a desired position to feed the picked sheet into fixed pinch rollers.
U.S. Pat. No. 4,566,683 teaches the controlling of the puffer air to vary the quantity in accordance with the weight or pressure of the documents on the table.
These prior art document picking devices can be adjusted to operate fairly dependably when the document in the stack have the same dimensions thickness, and weight, i.e., the document stack is homogenous, uniform, and predictable. Nonhomogeneity of the document stack can also result from variations in the lengths and widths of the documents to be fed even if the document are of the same thickness and weight. Such feeders, however, become less reliable and even inoperable when the document stack is nonhomogenous and nonuniform. The characteristics of individual documents in the stack are no longer predictable resulting in document behavior that hinders or prevents dependable feeder operation. For example, heavy documents may not be moved high enough by the puffer air for the picker mechanism to attach them. Light weight documents may be moved higher than practical for good operation.